G.f.: exp( Sum_{n>=1} 2^A090740(n) * x^n/n ) where A090740(n) = highest exponent of 2 in 3^n-1.

Terms

a(0) =1a(1) =2a(2) =6a(3) =10a(4) =22a(5) =34a(6) =62a(7) =90a(8) =150a(9) =210a(10) =326a(11) =442a(12) =654a(13) =866a(14) =1230a(15) =1594a(16) =2198a(17) =2802a(18) =3766a(19) =4730a(20) =6230a(21) =7730a(22) =9998a(23) =12266a(24) =15630a(25) =18994a(26) =23878a(27) =28762a(28) =35742a(29) =42722